This invention is in the field of position sensors, and specifically relates to magnetic position sensors for use with automotive suspension systems.
Position sensors of all types are commonly known in the art, especially in the automotive and industrial environments. Position sensors determine the location of a movable part with respect to a reference. Such sensors range from complex electrical devices to simple mechanical devices. The prior art includes position sensing devices adapted for many different applications as well as position sensors specifically adapted for automotive suspension systems. Adjustable suspension systems typically utilize one or more sensors for detecting the position of one or more parts of the suspension system with respect to either another part of the suspension system or another part of the chassis of the vehicle.
There are many problems with the sensors available today. Sensors which provide only discrete signals can resolve a desired position into only a relatively small number of possibilities. Analog position sensing devices usually have a relatively short stroke or measuring distance.
A position sensing device using a magnetic sensor is disclosed in European Patent No. 0215454. The device of European Patent No. 0215454 has a relatively long stroke or measuring range, but the device is inadequate for use as a position sensing device in today's automotive suspension systems. The device consists of a closed magnetic circuit including at least one permanent magnet or electro-magnet, a yoke and a magnetic sensor. The sensor moves along an inside surface of the yoke and senses a magnetic field intensity of leakage flux emanating from the inside surface of the yoke. The sensor being transferred along the yoke surface makes the sensor vulnerable to a bumpy and harsh environment of an automobile. Furthermore, the design is too expensive and complex for use in an automotive suspension system that would use up to three or four sensors in one suspension system.
Another position sensor that measures magnetic field intensities is a device disclosed in European Patent No. 0368687A2. The device disclosed in European Patent No. 0368687A2 includes a magnetic tape which produces a magnetic field that varies sinusoidally along a longitudinal axis of the tape. The device includes a cursor acting as a pick up head and comprising two identical detectors each including a magnetic core shaped as a half torus and a magnetic flux to voltage transducer. The position of the cursor is a function of the distance between the two transducers and the magnetic field intensity detected. The use of two transducers and two magnetic cores each shaped as a half torus makes the device cumbersome and impractical in an automotive suspension system environment.
Today's automotive components are focusing on active and semiactive suspension systems that are safe, reliable and provide smooth transitions responsive to rough driving conditions and roads. One of the first attempts at such powerful suspension systems include complicated sensors that are expensive and require a significant amount of extra horsepower drained from the automobile's engine system. Such suspension systems add additional weight and intricate electronics to existing suspension systems. The systems are not practical for most car models especially the lower cost models.
Simple, low cost sensors that are being produced today are typically digital sensors. The digital devices simply gives a discrete high, medium and low signal, or a small number of discrete possible states, and the suspension system adjusts accordingly. Unfortunately, since the signal is simply a high or low signal or a discrete state, the signal is not representative of how far off the error is from an equilibrium position. There is the constant problem of over correcting or under correcting and a number of corrections will have to be made before equilibrium is found.
Thus, there is a need in the market for a simple, low cost position sensor that can be adapted for the automotive environment especially to provide suspension position information and other types of information for adjustable suspension systems.